Electron transfer across multiple hydrogen bonds: the case of ureapyrimidinedione-substituted vinyl ruthenium and osmium complexes.
Electron transfer across multiple hydrogen bonds: the case of ureapyrimidinedione-substituted vinyl ruthenium and osmium complexes.
复制标题
DOI：
10.1021/ja809566g
复制
发表时间：
2009-04
影响因子：
15
通讯作者：
M. Pichlmaier;R. Winter;M. Zabel;S. Záliš
中科院分区：
文献类型：
--
作者：
M. Pichlmaier;R. Winter;M. Zabel;S. Záliš
钌和锇络合物 2a,b 和 3a,b 具有 N-4,6-二氧代-5,5-二丁基-或 N-4,6-二氧代-5,5-二-(2-丙烯基)-1,4,5,6-四氢嘧啶-2-基-N'(4-乙烯基苯基)-脲配体，通过自互补四元体二聚氢键供体/供体/受体/受体（DDAA）基序。我们提供的证据表明，二聚体结构在非极性溶剂和 0.1 M NBu(4)PF(6)/CH(2)Cl(2) 支持电解质溶液中保持不变。所有配合物在两次连续的双电子氧化（DeltaE(1/2) 大约 = 500 mV）中被可逆氧化，单个氢桥氧化还原活性部分的氧化没有任何可辨别的电位分裂。红外和紫外/可见/近红外光谱电化学显示中性到双阳离子的一步转化，没有任何中间单氧化自由基阳离子的明显特征。参与氢键的 NH 和 CO 基团的氧化引起的 IR 变化仅限于苯乙烯基键合的脲 NH 功能。红外波段分配由量子化学计算辅助。我们的实验结果清楚地表明，至少在目前的系统中，脲嘧啶二酮 (Upy) DDAA 氢键基序不支持电子转移。明显的原因是两个氢键官能团都没有对占据的前沿能级做出贡献。这导致近简并的 MO 对，代表各个单体构建块的同相和异相组合。
Ruthenium and osmium complexes 2a,b and 3a,b featuring the N-4,6-dioxo-5,5-dibutyl- or the N-4,6-dioxo-5,5-di-(2-propenyl)-1,4,5,6-tetrahydropyrimidin-2-yl-N'(4-ethenylphenyl)-urea ligand dimerize by a self-complementary quadruply hydrogen-bonding donor/donor/acceptor/acceptor (DDAA) motif. We provide evidence that the dimeric structures are maintained in nonpolar solvents and in 0.1 M NBu(4)PF(6)/CH(2)Cl(2) supporting electrolyte solution. All complexes are reversibly oxidized in two consecutive two-electron oxidations (DeltaE(1/2) approximately = 500 mV) without any discernible potential splitting for the oxidation of the individual hydrogen-bridged redox active moieties. IR and UV/vis/NIR spectroelectrochemistry show a one-step conversion of the neutral to the dication without any discernible features of an intermediate monooxidized radical cation. Oxidation-induced IR changes of the NH and CO groups that are involved in hydrogen bonding are restricted to the styryl-bonded urea NH function. IR band assignments are aided by quantum chemical calculations. Our experimental findings clearly show that, at least in the present systems, the ureapyrimidinedione (Upy) DDAA hydrogen-bonding motif does not support electron transfer. The apparent reason is that neither of the hydrogen-bonding functionalities contributes to the occupied frontier levels. This results in nearly degenerate pairs of MOs representing the in-phase and out-of-phase combinations of the individual monomeric building blocks.